The present invention relates to stripper fingers and associated mounts used with a fuser, such as for xerographic printers.
In xerographic or electrostatographic printers commonly in use today, a charge-retentive member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the charge-retentive surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the original document. Subsequently, the electrostatic latent image on the charge-retentive surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the charge-retentive area to form a powder image on the charge-retentive area. This image is subsequently transferred to a sheet, such as copy paper, to which it is permanently affixed by heating or by the application of pressure. Following transfer of the toner image to the sheet, the charge-retentive member is cleaned of any residual toner that may remain thereon in preparation for the next imaging cycle.
One approach to fixing the toner image is by applying heat and pressure by passing the sheet containing the unfused toner images between a pair of opposed roller members at least one of which is internally heated. During this procedure, the temperature of the toner material is elevated to a temperature at which the toner material coalesces and becomes tacky. This heating causes the toner to flow to some extent into the fibers or pores of the sheet. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to become bonded to the support member. Typical of such fusing devices are two roll systems wherein the fuser roll is coated with an adhesive material such as a silicone rubber or other low surface energy elastomers.
During the fusing process and despite the use of low surface energy materials as the fuser roll surface, there is a tendency for the print substrate to remain tacked to the fuser roll after passing through the nip between the fuser roll and the pressure roll. When this happens, the tacked print substrate does not follow the normal substrate path but rather continues in an arcuate path around the fuser roll, eventually resulting in a paper jam which will require operator involvement to remove the jammed paper before any subsequent imaging cycle can proceed. As a result it has been common practice to ensure that the print substrate is stripped from the fuser roll downstream of the fuser nip. One approach is the use of a plurality of stripper fingers placed in contact with the fuser roll to strip the print substrate from the fuser roll. While satisfactory in many respects, this suffers from difficulties with respect to both fuser roll life and print quality. To ensure an acceptable level of stripping it is frequently necessary to load such a stripper finger against the fuser roll with such a force and at such an attack angle that there is a tendency to peel the silicone rubber off the fuser roll, thereby damaging the roll to such an extent that it can no longer function as a fuser roll.
The present invention is directed to an improved design of a stripper finger and associated mounting structure.
U.S. Pat. No. 4,062,534 discloses a fusing apparatus in which a plurality of rigid stripping pawls are urged against a fuser roll. For each pawl, a spring directly urges the pawl against the roll.
U.S. Pat. No. 4,796,880 discloses a fusing apparatus in which a xe2x80x9cskivexe2x80x9d is used to strip sheets from the fuser roll. The skive is a metal plate which is urged against the roll by its own spring constant.
U.S. Pat. No. 5,448,347 discloses a mounting arrangement for a skive used to strip sheets from a fuser roll. The skive is mounted on a flexible mounting, and further defines a guide surface for directing the stripped sheet along a post-fuser path.
U.S. Pat. No. 5,822,668 discloses a fuser module which pivots open for jam clearance. Rigid stripper fingers are urged against the fuser roll. When the module is pivoted open, the stripper fingers disengage from the fuser roll and land on a stop within the module. As the module is re-closed, contours associated with the stripper finger follow the stop so that the stripper finger is properly set back on the fuser roll without spiking the fuser roll.
U.S. Pat. No. 6,029,039 discloses a retractable skive assembly. Each rigid skive is urged against a surface of the fuser roll by a spring. The skive and spring are mounted on a retractor which disengages the skive from the roll for manual paper jam clearance.
It is known in the prior art to mount flexible stripper fingers rigidly within a machine, so that the fingers are urged against a fuser roll exclusively by the spring force caused by deformation of the fingers.
According to one aspect of the present invention, there is provided a fusing apparatus useful in printing, comprising a fuser roll; a first stripper finger mount; spring means for urging the first stripper finger mount substantially toward the fuser roll and against a stop; and a first stripper finger mounted on the first stripper finger mount, the stripper finger contacting the fuser roll with a spring force when the first stripper finger mount is urged against the stop.